import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
public class InorderTraversal {
    public List<Integer> inorderRecursive(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        traverse(root, result);
        return result;
    }
    private void traverse(TreeNode node, List<Integer> result) {
        if (node == null) return;
        traverse(node.left, result);
        result.add(node.val);as
        traverse(node.right, result);
    }
}


public class InorderTraversal {
    public List<Integer> inorderIterative(TreeNode root) {
        List<Integer> result = new ArrayList<>();
        Stack<TreeNode> stack = new Stack<>();
        TreeNode curr = root;
        while (curr != null || !stack.isEmpty()) {
            while (curr != null) {
                stack.push(curr);
                curr = curr.left;
            }
            curr = stack.pop();
            result.add(curr.val);
            curr = curr.right;
        }
        return result;
    }
}

public class Main {
    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.left = new TreeNode(4);
        root.left.right = new TreeNode(5);
        InorderTraversal solution = new InorderTraversal();
        System.out.println("递归中序遍历结果: " + solution.inorderRecursive(root));
        System.out.println("非递归中序遍历结果: " + solution.inorderIterative(root));
    }
}